Urinary tract infections are one of the most common bacterial infections in the U.S. Proteus mirabilis, a member of the Enterobacteriaceae, is a major cause of infection in individuals with complicated urinary tracts. Although several virulence factors have been identified in P. mirabilis, the recent completion of the sequencing of this genome has the potential to greatly increase our understanding of P. mirabilis pathogenesis. Fimbriae, structures that extend from the bacterial cell surface, are often involved in colonization and disease progression. Remarkably, 17 potential chaperone-usher fimbriae were annotated by us in the P. mirabilis genome, only five of which had been previously identified. The first Specific Aim of this proposal is to study general expression characteristics of these fimbriae, and to choose one of the novel fimbriae to study in further detail. RT-PCR, microarray analysis of genes expressed during experimental urinary tract infection in a mouse model, and mass spectrometry of surface-expressed proteins will be used to hone in on a functional fimbria relevant to the disease process. Knockout and overexpression studies will be employed to elucidate the function of the fimbria using assays including adherence to cell culture or extracellular matrix components and experimental infections of the murine urinary tract. Ten of the 17 potential fimbrial operons in P. mirabilis contain a gene encoding a transcriptional regulator. The majority of these regulators, identified by their homology to mrpJ in the mrp fimbrial operon, inhibit flagellar motility. Preliminary results suggest that mrpJ paralogs likely also regulate other functions, including expression of other fimbriae. The second Specific Aim of this proposal focuses on the mrpJ paralog associated with the fimbria outlined in Specific Aim 1. Overexpression and knockout strains of the mrpJ paralog will be coupled with microarray studies and analysis of known fimbriae. Data gained from these studies will not only increase our knowledge about P. mirabilis pathogenesis and potentially lead to new measures against UTIs, but also will be relevant to other pathogens of mucosal surfaces. The bacterial pathogen Proteus mirabilis can cause debilitating disease in the urinary tract, including the formation of bladder and kidney stones. Our recent completion of the P. mirabilis genome sequence led to the discovery of many previously unknown, potential virulence factors. The goal of this project is to study how one of these virulence factors might contribute to the disease process.